1. Field of the Invention
The present invention relates to a method for forming a raised source/drain semiconductor device, and more particularly to a method for forming a local-halo semiconductor device with raised source/drain.
2. Description of the Prior Art
As semiconductor devices are scaled to smaller dimensions, generally in the sub-0.1 xcexcm region, it is highly desirable and generally necessary to fabricate such devices with source/drain shallow junction and a controllable halo implant region adjacent to the source/drain shallow junction to reduce short channel effects, such as subsurface punchthrough and hot carrier effect. The halo implant region is a doped implanted region, which is oppositely doped to the shallow junction region. However, when a silicide is formed on the source/drain region, the silicide easily contacts with the shallow junction to make junction leakage. Therefore, an approach to resolve the leakage problem is to use raised source/drain. Since the raised source/drain is formed upward above the substrate, the silicide could not easily contact with the shallow junction, and then the junction leakage can be reduced.
FIGS. 1A to 1C shows various steps for forming a conventional N-channel metal-oxide-semiconductor (MOS) device with raised source/drain. The conventional method comprises the following steps. Firstly, referring to FIG. 1A, a P type semiconductor substrate 100 is provided. A plurality of shallow trench isolation 101 is formed in the substrate 100. Then, a gate oxide 102 and a gate electrode 103 are sequentially formed between each pair of the shallow trench isolation 101 on the substrate 100. Subsequently, placing an implant mask on the substrate 100 and by way of ion implantation, to form an N type lightly doped drain region 104 between the gate electrode 103 and each of the pair of shallow trench isolation 101 in the substrate 100. And then, performing halo implantation to form a halo implant region 105 with P type conductivity surrounding each of the lightly doped drain region 104.
Secondly, referring to FIG. 1B, forming a conformal silicon dioxide layer 106 on the gate electrode 103 and then forming a silicon nitride layer 107 on the conformal silicon dioxide layer 106. The conformal silicon dioxide layer 106 is anisotropically etched by way of reactive ion etch method to form a pair of first sidewall spacers 106 on opposite sides of the gate electrode 103 and a pair of second sidewall spacers 107 on the opposite sides of the first sidewall spacer 106.
Finally, referring to FIG. 1C, forming a raised source/drain 108 upward on each of the pair of the lightly doped drain region 104. However, there are some disadvantages existing in this conventional method. One is the halo implant region 105 surrounding the lightly doped drain region 104 increases the junction capacitance, resulting in a slower operation speed for the MOS device. The other is the misalignment of the ion implant mask can cause changeable LDD/halo implant regions.
Accordingly, it is desirable to provide a method for forming a local halo MOS device with raised source/drain to reduce the junction capacitance and also overcome the drawbacks of the conventional method.
It is an objective of the present invention to provide a method for forming a self-aligned local-halo metal-oxide-semiconductor (MOS) device with raised source/drain, in which a gate electrode and the raised source/drain act as the self-aligned masks, a LDD/halo implantation is performed to form a local LDD/halo diffusion region therebetween in the substrate. The local LDD/halo diffusion region reduces the junction capacitance. Thereby, the operation speed of the MOS device is facilitated.
Another objective of the present invention is to provide a method for forming a self-aligned local-halo metal-oxide-semiconductor (MOS) device with raised source/drain, in which a gate electrode and the raised source/drain act as self-aligned masks to form a local LDD/halo diffusion region therebetween. Therefore, an extra mask is not necessary and then the manufacturing process is simplified.
In order to achieve the above objectives, the present invention provides a method for forming a self-aligned local-halo metal-oxide-semiconductor device. At first, a semiconductor substrate with a first conductive type having a plurality of shallow trench isolation formed therein is provided. Then, sequentially forming a gate oxide and a gate electrode between each pair of the shallow trench isolations over the substrate. Next, forming a first sidewall spacer along each side of the gate electrode. And then, a second sidewall spacer is formed along one side of each first sidewall spacer. Thereafter, forming a raised source/drain upward on the substrate between each shallow trench isolation and each second sidewall spacer. Then, each second sidewall spacer is removed. Following, forming a lightly doped diffusion region with a second conductive type being opposite with the first conductive type between each raised source/drain and the gate electrode in the substrate. Finally, forming a halo diffusion region with the first conductive type surrounding the lightly doped diffusion region. By way of the present method, a local LDD/halo diffusion region with a low junction capacitance is obtained. And then, the operation speed of the MOS device is facilitated.